EL5 - Molecules of life

• Covalent bonding


  The sharing of electrons between atoms
• Bonding pairs


  pairs of electrons shared between the atoms
• Lone pairs


  Pairs of electrons not used in bonding
• Double bonds


  When 2 pairs of electrons are shared in a covalent bond (e.g. in O2)
• Triple bonds


  When 3 pairs of electrons are shared in a covalent bonds (e.g. in N2)
• Dative covalent bonds


  When both electrons in a bonding pair has come from the same atom
• In a stick diagram, how is a dative covalent bond shown?


  An arrow instead of a line pointing away from the donating atom
• Properties of covalently bonded simple molecules


  - covalent intramolecular bonds within simple molecules are strong

  - intermolecular forces between molecules are weak

  - low melting and boiling point
• Intramolecular forces


  - forces within the molecules caused by the attraction and repulsion of charged particles

  - strong
• Intermolecular forces


  - forces of attraction between molecules due to charged particles

  - weak
• Why is the boiling point higher than the melting point?


  - only some bonds are required to be broken to melt a substance

  - all bonds are required to be broken to boil a substance

  - more energy is required
• Valence repulsion theory


  Electron pairs move as far apart as possible due to their mutual repulsion
• Regularly shaped molecules


  Only have bonding groups of electrons
• 2 groups of electron (regular)


  Linear - 180º
• 3 groups of electrons (regular)

  Trigonal planar - 120º
• 4 groups of electrons (regular)

  Tetrahedral - 109.5º
• 5 groups of electrons (regular)

  Trigonal bipyramidal - 90º and 120º
• 6 groups of electrons (regular)

  Octahedral - 90º
• 3 bonding 1 lone pair

  Trigonal bipyramidal - 107º
• 2 bonding 2 lone pairs


  Bent shape - 104.5º
• How are bonds in front of the plane represented?


  A solid triangle
• How are bonds behind the plane represented?


  A dotted line